Merge to 54: On the Mac, AX_EVENT_LOAD_COMPLETE should only be fired on the top document.

content/browser/accessibility/browser_accessibility_manager_mac.mm

Index: content/browser/accessibility/browser_accessibility_manager_mac.mm
diff --git a/content/browser/accessibility/browser_accessibility_manager_mac.mm b/content/browser/accessibility/browser_accessibility_manager_mac.mm
index b2dff5cf91602e237a02682f2ad1f5baf62a74f6..77ce72f4df5882ac45c0533656d8cbfffcdd961b 100644
--- a/content/browser/accessibility/browser_accessibility_manager_mac.mm
+++ b/content/browser/accessibility/browser_accessibility_manager_mac.mm
@@ -191,7 +191,14 @@ void BrowserAccessibilityManagerMac::NotifyAccessibilityEvent(
       mac_notification = NSAccessibilityLayoutCompleteNotification;
       break;
     case ui::AX_EVENT_LOAD_COMPLETE:
-      mac_notification = NSAccessibilityLoadCompleteNotification;
+      // This notification should only be fired on the top document.
+      // Iframes should use |AX_EVENT_LAYOUT_COMPLETE| to signify that they have
+      // finished loading.
+      if (IsRootTree()) {
+        mac_notification = NSAccessibilityLoadCompleteNotification;
+      } else {
+        mac_notification = NSAccessibilityLayoutCompleteNotification;
+      }
       break;
     case ui::AX_EVENT_INVALID_STATUS_CHANGED:
       mac_notification = NSAccessibilityInvalidStatusChangedNotification;